Response of vegetation to flooding

Excessive rainfall in much of Kansas in 2019 has caused flooding. Vegetation response to flooding depends primarily on duration and frequency. Flooding impacts the amount of oxygen, carbon dioxide, temperature, and light available for photosynthesis. Impeded gas exchange results in a depletion of carbohydrate reserves, reduced energy available to the plant, disrupts cells, and impairs nutrient uptake, resulting in plant death. Loss of vegetation is also temperature dependent. It takes fewer days of submergence to cause stand loss as soil temperatures increase.

Considerable variation exists among native grasses in their tolerance to inundation. Little bluestem tolerates only brief periods of flooding (3-6 days). Big bluestem and Indiangrass will tolerate only 7-14 days of flooding, whereas switchgrass tolerates 15-30 days. Eastern gamagrass will tolerate 10-22 days. Although buffalograsss is shorter than most species it will tolerate 45-90 days of inundation. A lowland species that is known to tolerate greater than 49 days of flooding is reed canarygrass.

Some invasive species such as yellow bluestem (3-6 days) and sericea lespedeza (10 days) have limited flood tolerance.

Flooding may indeed kill or damage many species, but certain species may survive. Sand deposition and lack of vegetative cover may require reseeding of flood-damaged areas. Consider planting species that are more tolerant of flooding, especially frequently flooded sites.

Figure 1. Pasture flooded in May 2019. Depth finder indicated 12 feet of water in the center of the native range/ 50% fescue pasture. Water standing on the surface for 25 days.Figure 2. Same pasture as Figure 1 one month after water receded. Before the flood. the pasture contained heavy grass and forbs, numerous cedar trees and no bare spots. Post flood, the cedars trees and other brushy plants appear dead. Reed canary grass and other marsh grasses represent current forage growth visible.Figure 3. Fescue pasture that was underwater for up to 18 days. Area towards the back of the photo had water up to base of hunting blind, 10 ft off the ground. Now, forage composition predominately reed canary grass. Brush and cedar trees do not seem to be impacted in this area. In foreground, uphill side of pasture was underwater for 10 days and still has solid stand of fescue and forbs.